I think that the Netmax software goes for around US100.00 retail, but there
are a number of free implementations...one that comes to mind is the Free
Cisco project at http://www.freesco.org. It's supposed to allow you to boot
a fully functional Linux router/firewall from a single floppy disk.  Since I
haven't tried it, I can't vouch for it, but it's reputed to be a pretty good
performer.